The present invention relates generally to systems and techniques for controlling the operation of an internal combustion engine, and more specifically to such systems wherein the efficacy of such control is based on the accuracy of fuel system related operating parameters.
Modern high pressure fuel systems for internal combustion engines typically employ sophisticated control techniques for monitoring and controlling multiple fuel system operating parameters including, for example, fuel supply pressure, injection pressure, engine timing, rate shape, injected fueling, and the like. However, even with such advanced control techniques, engine-to-engine (between-engine) variations are known to exist in at least some of the typically monitored fuel system operating parameters. For example, many high pressure fuel and/or engine control systems are sensitive to between-engine variations in engine static timing and pump phasing as well as overall system bandwidth. For purposes of the present invention, an engine static timing error is defined as any difference between a measured engine reference position (e.g., top-dead-center or TDC) and the actual reference position, which may vary from engine to engine, and a fuel pump phasing error is defined as any difference between a fuel pump reference position and a corresponding engine reference position.
As one particular example of the foregoing problem, engine static timing errors are known to be a significant contributor to variations in start-of-injection (SOI) in known fuel control systems. As another example, although accurate fuel supply pressure sensors and engine position sensors are widely used in high pressure fuel control systems, such between-engine variations typically exist with regard to the placement of peak supply pressures relative to a reference engine position. More specifically, fuel pumps in cyclic, high pressure fuel control systems would typically be controlled such that fuel supply pressure peaks are expected to occur at some predefined crank angle relative to a reference crank angle (e.g., top-dead-center or TDC) for each cylinder at a given engine speed. However, due to between-engine variations in engine static timing and fuel pump phasing, such fuel supply pressure peaks have been found to deviate from the predefined crank angle by fixed amounts or offsets from engine to engine. Similarly, due to between-engine variations in overall system bandwidth, such fuel supply pressure peaks have also been found to deviate from the predefined crank angle by variable amounts as a function of engine speed.
Minimizing such variations by conventional mechanical means requires tightening tolerances or system specifications, both of which typically result in increased system cost. What is therefore needed is a strategy for quantifying and compensating for between-engine variations in engine static timing and fuel pump phasing and overall system bandwidth that does not require additional hardware components and generally does not increase system cost. Ideally, such a strategy should further provide for more accurate fuel system operating parameter monitoring and control, and further provide for improved diagnostic capabilities.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, an apparatus for determining errors in monitored operating parameters of a fuel system for an internal combustion engine comprises means for sensing a pressure associated with a fuel system of an internal combustion engine and producing a pressure signal corresponding thereto, the pressure signal having peak values corresponding to peak pressure values thereof, means for sensing a reference position of the internal combustion engine and producing a reference position signal corresponding thereto, means for determining first and second engine positions at which peak values of the pressure signal occur at first and second engine speeds, and means for determining a first operating parameter error value as a function of the first and second engine positions relative to the engine position.
In accordance with another aspect of the present invention, an apparatus for determining errors in monitored operating parameters of a fuel system for an internal combustion engine comprises a pressure sensor for sensing a pressure associated with a fuel system of an internal combustion engine and producing a pressure signal corresponding thereto, wherein the pressure signal has peak values corresponding to peak pressures thereof, an engine position sensor producing a reference position signal corresponding to a reference position of the internal combustion engine, and a control circuit responsive to the pressure signal for determining a first engine position at which a peak value of the pressure signal occurs. The control circuit is further operable to determine an operating parameter error value as a function of the first engine position relative to the reference engine position.
In accordance with a further aspect of the present invention, a method of determining errors in monitored operating parameters of a fuel system for an internal combustion engine comprises the steps of sensing a pressure associated with a fuel system of an internal combustion engine and producing a pressure signal having peak values corresponding thereto, sensing a reference position associated with the operation of the internal combustion engine, determining an offset value as a difference between an engine position at which peak values of the pressure signal occur and the reference engine position, and determining an operating parameter error value as a function of the offset value.
One object of the present invention is to provide a strategy for determining engine static timing errors and overall system bandwidth.
Another object of the present invention is to provide such a strategy for determining engine static timing, high pressure fuel pump phasing and overall hydro-mechanical system bandwidth errors relating to a fuel control system of an internal combustion engine.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.